This invention relates to optical components generally, that is components which operate in the optical domain. Such components are designed for use in various systems which utilize optical fibers, such as optical communications systems, optical data processing systems and optical switching systems. Specifically, this invention pertains to an optical shift register.
The development of optical fiber and optical semiconductor technologies in recent years has made possible various types of optical communications systems and optical switching systems. To utilize the full bandwidth and speed available in optical systems, it has become necessary to design and fabricate optical logic and switching components which eliminate the necessity for electrical-to-optical and optical-to-electrical conversions.
Electronic shift registers have played a major role in digital electronic systems for many decades. Numerous electronic systems and subsystems have been based on electronic shift registers. Typical examples are digital delay lines, serial-to-parallel and parallel-to-serial converters, counters, random access memories and electronic switching systems. Despite the rapid development of optical fiber technology, optical shift registers have received only scant attention. This phenomenon is due primarily to the fact that electronic systems have improved rapidly over time and always seemed to be sophisticated enough to meet the needs of the telecommunications industry. However, the deployment of optical fibers for information transmission has necessitated a different approach to this problem. At present, the high bandwidth advantage of optical fibers is still not fully utilized because electronic switching systems are not fast enough for high speed and high throughput optical switching. To solve this problem, the switching functions must be performed in the optical domain, eliminating the optical-to-electrical and electrical-to-optical conversions.
Two embodiments of an optical shift register are disclosed in U.S. Pat. No. 4,761,060. In one embodiment, the optical shift register comprises a series of optical D flip-flops connected in cascade through light branching circuits. In the other embodiment, the optical D flip-flops are connected in tandem through branching circuits and use optical waveguide switches within the flip-flops. The optical shift registers disclosed in this patent require an optical bistable element, have critical and somewhat inflexible timing requirements and have a relatively complex structure.